1. Field of the Invention
The present invention relates generally to a pulverulent material feeder apparatus. More particularly, the present invention is concerned with a pulverulent material feeder apparatus which includes an inner cylinder and an outer cylinder disposed coaxially on a bottom plate and in which a pulverulent material such as powder, pulverized materials, particles or the like heaped at an angle of rest is expelled or extruded radially and outwardly from the inner cylinder through a gap defined underneath a lower edge of the inner cylinder, whereupon the pulverulent material is then discharged from a discharge port while being transported by means of revolving scraping members or blades at a substantially constant discharge or feed rate.
2. Description of the Prior Art
In the pulverulent material feeder apparatus known heretofore, an annular space for transportation of a pulverulent material is defined between an outer cylinder and an inner cylinder disposed coaxially with each other, wherein a gap of a constant height is formed between a bottom plate of the outer cylinder and a lower edge of the inner cylinder so that a pulverulent material charged into the inner cylinder and heaped at an angle of rest is spontaneously collapsed and extruded radially outwardly into the material transporting space through the gap formed between the lower edge of the inner cylinder and the bottom plate, the pulverulent material being then moved circumferentially within and along the annular transporting space by scrapers or revolving blades to be continuously discharged under gravity through a discharge port formed in the bottom plate, to thereby supply or feed the pulverulent material to a succeeding process constantly at a predetermined discharge or feed rate.
However, in the pulverulent material feeder apparatus of the structure described above, it has been found that the amount or volume of pulverulent material extruded into the annular transporting space through the extrusion gap differs between a location immediately succeeding the discharge port and a location immediately preceding the discharge port, although it depends on particle sizes, shapes, fluidity and the like factors of the pulverulent material charged or supplied into the inner cylinder. More specifically, in a region immediately succeeding the discharge port, the amount of pulverulent material extruded through the gap tends to increase because of rapid formation of an angle of rest for stabilization in this region, resulting in the occurrence of a phenomenon in which the pulverulent material is extruded into the annular transportation space only through a gap portion which is located adjacent to the discharge port at the downstream side thereof with no material being expelled through the remaining gap portion. Of course, such phenomenon may depend on the physical properties of the material, as mentioned above.
This phenomenon obviously contradicts a first-in/first-out uniform feed principle which requires as the premise that the pulverulent material accommodated within the inner cylinder is extruded or expelled through the gap uniformly over the whole circumference thereof, and thus gives rise to such undesirable situation that a heap of the pulverulent material charged in the inner cylinder may undesirably collapse nonuniformly.
Besides, in the pulverulent material feeder apparatuses of the prior art, the bottom is constituted by a flat plate extending horizontally. Consequently, extrusion efficiency becomes lowered as the volume of the pulverulent material within the inner cylinder decreases. Thus, a lot of time is required for completely discharging the material from the feeder apparatus, to a disadvantage. Additionally, another problem is encountered in that residuals of pulverulent material resting on the revolving blades by forming an angle of rest can not be cleared out therefrom.